///
// * jdbm LICENSE v1.00
// *
// * Redistribution and use of this software and associated documentation
// * ("Software"), with or without modification, are permitted provided
// * that the following conditions are met:
// *
// * 1. Redistributions of source code must retain copyright
// *    statements and notices.  Redistributions must also contain a
// *    copy of this document.
// *
// * 2. Redistributions in binary form must reproduce the
// *    above copyright notice, this list of conditions and the
// *    following disclaimer in the documentation and/or other
// *    materials provided with the distribution.
// *
// * 3. The name "jdbm" must not be used to endorse or promote
// *    products derived from this Software without prior written
// *    permission of Cees de Groot.  For written permission,
// *    please contact cg@cdegroot.com.
// *
// * 4. Products derived from this Software may not be called "jdbm"
// *    nor may "jdbm" appear in their names without prior written
// *    permission of Cees de Groot. 
// *
// * 5. Due credit should be given to the jdbm Project
// *    (http://jdbm.sourceforge.net/).
// *
// * THIS SOFTWARE IS PROVIDED BY THE ndbm PROJECT AND CONTRIBUTORS
// * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
// * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
// * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
// * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
// * OF THE POSSIBILITY OF SUCH DAMAGE.
// *
// * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
// * Contributions are Copyright (C) 2000 by their associated contributors.
// *
// * $Id: FileHeader.java,v 1.3 2005/06/25 23:12:32 doomdark Exp $
// 


//*************************************************************************
//**  Included in JDMB 1.0 port to SharpDBM;  11/2013 Cyrus Neah cneah@codingreal.com
//**  SharpDBM is an independent reimplementation of the JDBM 1.0 software library in C#  
//*************************************************************************

using SharpDBM.helper;

namespace SharpDBM.recman
{

///
// *  This class represents a file header. It is a 1:1 representation of
// *  the data that appears in block 0 of a file.
// 
	public class FileHeader : BlockView
	{
	// offsets
		private const short O_MAGIC = 0; // short magic
		private const short O_LISTS = Magic.SZ_SHORT; // long[2*NLISTS]
		private const int O_ROOTS = O_LISTS + (Magic.NLISTS * 2 * Magic.SZ_LONG);

	// my block
		private BlockIo block;

	/// The number of "root" rowids available in the file. 
		internal const int NROOTS = (RecordFile.BLOCK_SIZE - O_ROOTS) / Magic.SZ_LONG;

//    *
//     *  Constructs a FileHeader object from a block.
//     *
//     *  @param block The block that contains the file header
//     *  @param isNew If true, the file header is for a new file.
//     *  @throws IOException if the block is too short to keep the file
//     *          header.
//     
		public FileHeader(BlockIo block, bool isNew)
		{
			this.block = block;
			if (isNew)
				block.writeShort(O_MAGIC, Magic.FILE_HEADER);
			else if (!magicOk())
				throw new Error("CRITICAL: file header magic not OK " + block.readShort(O_MAGIC));
		}

	/// Returns true if the magic corresponds with the fileHeader magic. 
		private bool magicOk()
		{
			return block.readShort(O_MAGIC) == Magic.FILE_HEADER;
		}


	/// Returns the offset of the "first" block of the indicated list 
		private short offsetOfFirst(int list)
		{
			return (short)(O_LISTS + (2 * Magic.SZ_LONG * list));
		}

	/// Returns the offset of the "last" block of the indicated list 
		private short offsetOfLast(int list)
		{
			return (short)(offsetOfFirst(list) + Magic.SZ_LONG);
		}

	/// Returns the offset of the indicated root 
		private short offsetOfRoot(int root)
		{
			return (short)(O_ROOTS + (root * Magic.SZ_LONG));
		}

//    *
//     *  Returns the first block of the indicated list
//     
		internal virtual long getFirstOf(int list)
		{
			return block.readLong(offsetOfFirst(list));
		}

//    *
//     *  Sets the first block of the indicated list
//     
		internal virtual void setFirstOf(int list, long @value)
		{
			block.writeLong(offsetOfFirst(list), @value);
		}

//    *
//     *  Returns the last block of the indicated list
//     
		internal virtual long getLastOf(int list)
		{
			return block.readLong(offsetOfLast(list));
		}

//    *
//     *  Sets the last block of the indicated list
//     
		internal virtual void setLastOf(int list, long @value)
		{
			block.writeLong(offsetOfLast(list), @value);
		}

//    *
//     *  Returns the indicated root rowid. A root rowid is a special rowid
//     *  that needs to be kept between sessions. It could conceivably be
//     *  stored in a special file, but as a large amount of space in the
//     *  block header is wasted anyway, it's more useful to store it where
//     *  it belongs.
//     *
//     *  @see #NROOTS
//     
		internal virtual long getRoot(int root)
		{
			return block.readLong(offsetOfRoot(root));
		}

//    *
//     *  Sets the indicated root rowid.
//     *
//     *  @see #getRoot
//     *  @see #NROOTS
//     
		internal virtual void setRoot(int root, long rowid)
		{
			block.writeLong(offsetOfRoot(root), rowid);
		}
	}

}